Coastal Erosion on Sydney’s southern beaches

Study Report

at the Water Research Laboratory of the University of New South Wales, Sydney, Australia

in association with the Bergische Universität Wuppertal Univ.-Prof. Dr.-Ing. H. Kaldenhoff

by cand.-Ing. Marcus Dätig

Sydney, January 2001 Contents

1 Introduction 1

2 Beaches in the coastal zone 2

3 The Beach System 5

4 Coastal erosion and beach processes 6

5 Human Response to Natural Coastal Hazards 9 5.1 The Establishment of Buffer Zones ...... 9 5.2 Beach Protection Systems ...... 9 5.2.1 Seawalls ...... 9 5.2.2 Groynes ...... 10 5.3 Sand Nourishment ...... 10 5.4 Dune Stabilization ...... 10

6 Three Southern Beaches of Sydney 13 6.1 Clovelly Beach ...... 14 6.2 Coogee Beach ...... 15 6.3 Maroubra Beach ...... 16

7 The Coastline Hazards of these beaches 20 7.1 Clovelly Bay ...... 20 7.1.1 Zone 1: hazard level: minor to moderate ...... 20 7.1.2 Zone 2: hazard level: minor to serious ...... 20 7.1.3 Zone 3: hazard level: minor ...... 21 7.1.4 Zone 4: hazard level: minor to serious ...... 22 7.1.5 Zone 5: hazard level: low ...... 22

i CONTENTS ii

7.2 Coogee Bay ...... 23 7.2.1 Zone 1: hazard level: minor ...... 23 7.2.2 Zone 2: hazard level: serious ...... 24 7.2.3 Zone 3: hazard level: minor ...... 25 7.2.4 Zone 4: hazard level: moderate to serious ...... 25 7.3 Maroubra Bay ...... 26 7.3.1 Zone 1: hazard level: moderate ...... 26 7.3.2 Zone 2: hazard level: serious ...... 27 7.3.3 Zone 3: hazard level: moderate to serious ...... 28 7.3.4 Zone 4: hazard level: minor to moderate ...... 28 7.3.5 Zone 5: hazard level: minor to moderate ...... 29 7.4 Final Statement ...... 29

Bibliography 31 List of Figures

2.1 Coastal Environment and processes ...... 2 2.2 Sediment gain and Sediment loss ...... 3

3.1 The Beach system ...... 5

4.1 Generation and Propagation of a wave ...... 6 4.2 Swell and Storm Profile ...... 7

5.1 Description of a Buffer Zone ...... 12

6.1 Location of the southern beaches ...... 13 6.2 Coogee beach subdivided in different areas ...... 16 6.3 Maroubra Beach, part of the ’Plan of Management’ ...... 19

7.1 Zones of the Clovelly Bay ...... 21 7.2 Clovelly Bay ...... 22 7.3 Clovelly Beach ...... 23 7.4 Zones of the Coogee Bay ...... 24 7.5 Coogee Beach, view from the south ...... 25 7.6 Coogee Bay, view from the north ...... 26 7.7 Zones of the Maroubra Beach ...... 27 7.8 Maroubra Beach ...... 28 7.9 Maroubra coast ...... 29

iii 1 Introduction

This report about the 3 southern beaches of Sydney starts by giving a brief introduction about the coast of New South Wales. The state of NSW is located in the southeast of Australia and is one of the oldest and most populated states in Australia. Consisting of an area of 801.506 square kilometres, which can be regarded as only 10 % of the whole continent, approximately 30% of the Australian inhabitants live there. The New South Wales coast extends from Tweed Heads in the north to Cape Howe in the south, a distance of 1590 km. Sixty percent of the coast, or 975 km consists of 721 sandy beaches. The other 615 km can mostly be described as rocky coast. The beaches range from long sweeping beaches on the north coast, up to 26 km in length, to small often deeply embayed beaches, many only a few meters in lengths. The coastal region of Sydney north for example with a length of 45 km has got 20 sandy beaches with an average length of 625m, compared to the coastal region south of Sydney, being 46 km long, but showing just an average length of 359m within 19 sandy beaches (1). Coastal Protection and coastal management being neglected in the early years of our century, by the 1960s it was becoming evident that coastal erosion and its effects are a serious problem. Private homes, commercial buildings, public facilities and even roads were all endangered. The New South Wales government initiated an investigation in which a study had been made about the coastal processes regarding the coastal recession. This study revealed average rates of coastal recession of 0.5 to 1.0 meter a year, an amount of the coast to be lost in the ocean, which is quite threatening. This study has been one of several reasons why the New South Wales government introduced the Beach Improvement Programme in 1975 to assist local authorities in restoring and improving the recreational amenity of the state’s beaches. This program was based upon technical work carried out by the Public Work Department (nowadays changed to the Department of Land and Water Conservation) and was used also as a means for increasing public awareness of coastal problems (2).

1 2 Beaches in the coastal zone

The coastal zone includes the underlying geology, the coastal hinterland, the inner continental shelf and the coastline including all coastal bays and beaches. The coastal environment is the most dynamic part of the earth surfaces. It contains elements of all spheres that make up earth namely the atmosphere, the hydrosphere, or ocean, the lithosphere, or geology and the biosphere. As the 4 spheres interact, (see figure 2.1) at the coast they produce a wide spectrum of coastal systems ranging from muddy tidal flats to rocky headlands to sandy beaches (2).

Figure 2.1: Coastal Environment and processes (1)

The atmosphere contributes the regional climate, the winds, rain and temperature and indirectly the ocean temperature. The hydrosphere determines sea level and due to this also the position of the shoreline, as well as contributing the major energy sources waves, tides and currents. Finally the biosphere includes the flora and fauna that inhabit either permanently, or in transit the coastal zone and contribute shell, coral and algal fragments that help to build the beaches. As this report will describe three of the sandy beaches of the southern beaches of Sydney, it first of all will show some facts about sandy beaches in general.

2 2 Beaches in the coastal zone 3

They consist of lithospheric elements namely sand lying ultimately on bedrock geology which is permanently been influenced by the interacting spheres mentioned above. Beaches form and change due to several processes that interact at the coast to produce beach systems. Two of those are to be regarded as climate and atmospheric processes. Climate interacting with the geology together with the physical forces of the rain let the part of the land surface runoff as well as rivers erode and transport sediment to the coast (2).

Figure 2.2: Sediment gain and Sediment loss (9)

At the coast it is also climate, particularly winds that interact with the ocean to generate waves and currents that are as already mentioned essential to build this sediment into beaches and dunes. Particularly on the coast of New South Wales the beaches are predominantly composed of quartz sand grains together with other rock fragments. These sediments originated in the coastal hin- terland. Over many millennia they have been delivered by rivers and streams, to the coast and continental shelf, and subsequently moved by waves on- or along-shore to be finally deposited as beaches and dunes (1). The regional geology therefore acts as a source for most of the sand on NSW beaches, the remainder being derived from shell and algal fragments. The rocks of the NSW coast that form the headlands and cliffs range in age from 500 million to 60 million years. As the coast is only 60 million years old, most of the rocks predate the coastline by many million years (1). Age of NSW coastal features: • Rocks: from 500 million years old • Beaches: from 12.000 years old • Most beaches: less then 6.500 years old The rock of the cliffs in the area that is going to be described in this report is known as the Hawkesbury Sandstone. It was laid down as sediment in a large river delta, which stretched 2 Beaches in the coastal zone 4 from north of the Hawkesbury River south almost to Nowra and west to lower Blue Mountains. This Sandstone was forming about 200 million years ago. The rock is made up mainly of sand and quartz in layers which vary according to what else the rivers brought down at different times and the way they were flowing. There is also an occasional band of shale, composed of more muddy material. Unlike the rock itself, the cliffs are very young regarding the geological time dimensions. During the last ice age the shoreline was about 12 km east, across the coastal plain. As the ice melted around the globe, sea level rose across the plain to plateaux of sandstone along the present shoreline. By the time it stopped rising about 6.000 years ago, the sea had flooded into a series of river valleys cut into this sandstone, creating bays and harbours along the new coast (1). 3 The Beach System

Different types of beaches show different types of profiles, depending on the influence of the littoral zone. The figure below illustrates a typical NSW beach system

Figure 3.1: The Beach system (2)

On the left hand side of figure 3.1 you can see the subaerial beach which is a dry zone above the shoreline, only influenced by the sea through storm waves, or when there are high tides being exceptionally high. The sediment on the subaerial beach becomes dry quickly and creates a series of coastal sand dunes with the help of wind, presupposing the coastline is nearly flat. Within the surf zone, containing bars troughs and breaking waves, some parts are exposed at low water when the tide is out and covered when the tide is in. The nearshore zone is permanently covered by water and extends seaward of the breakerzone out to the modal wave base. The wave base describes the point, regarding the figure shown above is approximately 20 m depth on the NSW coast, to which ocean waves can move beach sands. Seaward from the wave base lies the inner continental shelf with no explicit influence on the beach system (1).

5 4 Coastal erosion and beach processes

Coastal erosion is the result of a complex interaction of physical processes. Depending on the circumstances, the water motions of waves, tides, storm surge, and nearshore currents com- bine and interact with the coastal land, which in turn has considerable inherent variability. The primary agent in coastal erosion, the waves, generate nearshore currents, which in turn trans- port the beach sediments, a movement which results in a rearrangement of the shoreline with possible sites of erosion. Waves, who are, as in most cases, generated by winds blowing over the water surface, are important as energy-transfer agents. They first obtain their energy from winds, transfer it across the expanses of the oceans and then deliver it to the coastal zone where it can be the primary cause of erosion or can generate a variety of nearshore currents and sand transport patterns (3). The generation of the waves is primarily dependent upon three storm factors. First of all the speed of the wind, second the duration of the storm and last but not least the fetch area over which the storm occurs (see figure 4.1). The duration is important in that the longer the winds have been blowing, the greater the amount of energy that can be transferred to the growing waves. The fetch area has a similar effect, once the waves travel out of the storm area, they no longer acquire additional energy. That means, the larger the fetch area, the more energy the waves can potentially obtain.

Figure 4.1: Generation and Propagation of a wave

By a process called wave dispersion, the highest-period waves in the spectrum where the storm takes place, means the fetching area, move out rapidly and would be the first to arrive and be measured at some distant coastal site. In other words, you can say, that the complex sea in the storm area is progressively transformed into regular swell waves as you can also see in the "Propagation period" of figure 4.1. These swell waves are known to travel over the expanse of the oceans with relatively little loss of energy. Important to the coastal erosion, the energy the waves have obtained from winds is thereby efficiently carried to the nearshore zone where

6 4 Coastal erosion and beach processes 7 it expended over a relatively narrow area. Reaching from the offshore to the nearshore zone the wave crests become narrower and peaked, the troughs becoming wide and flat (3). Due to a decrease in the wave length and an increase in the wave height, eventually the waves oversteepen, become unstable and break, generally either by plunging or spilling. The nature of their breaking depends on their initial steepness and on the slope of the beach. By breaking on the shore, the ’wave swash’ pushes sediment up to the beach face, which is dragged back due to the ’backwash’. Because of the water percolating into the surface, the backwash can’t take as much water back as the swash brought up to the beach face. Therefore the onshore movement of sediment is higher than the backshore movement, until the slope reaches a state of dynamic equilibrium. Having reached this state, the same amount of sediment is moved landwards as is returned seawards. The amount of the percolating water depends primarily on the size of the grain. Hence the size of the grain influences the time it takes to reach the state of the dynamic equilibrium. Usually you can say, the coarser the sediment grain size, the steeper the overall beach-slope. On steep, coarse-sand to cobble beaches the waves normally break directly at the base of the beach face and swash up the slope, a surf zone with a bar being almost completely absent. The beach profile also depends on the wave energy level. Steep-wave conditions tend to shift sand offshore, eroding it from the beach berm and depositing it into bars in the region of the breaker zone. The swash of a steep wave breaking onto the beach does not move far up the beach. Consequently, less energy is lost in transporting the sediment up to the beach, as well as less percolation of the water into the sand can take place. Therefore sediment can be moved seawards. The sand removed from the beach is normally deposited offshore, to be slowly returned to the beach during periods of calm weather and constructive waves. If an area is affected by several storm surges during a season, then the beach may not have enough time to recover, and erosion of the beach is cumulative (2). The different wave energy level that may occur on the coast, depend on the time of the year. Wave heights tend to be larger during the storms periods, producing a change in the beach profile, in so far that the sediment is removed from the beach face and transported seawards to build the longshore bar (see figure 4.2. During the periods with predominantly swell waves the sediment of the bar is moved back landwards to reconstruct the beach berms. But nevertheless such changes between the so called swell and storm profile, are important to coastal erosion, because the loss of the berm in the storm period profile permits the wave swash to more directly attack the coastal property.

Figure 4.2: Swell and Storm Profile 4 Coastal erosion and beach processes 8

Another aspect concerning coastal erosion has to be mentioned as the storm surge. It is caused by meteorological factors such as strong winds and abrupt atmospheric pressure reduction lead- ing to a significant change in the water level. The rise in water level mostly is rather abrupt, induced by strong onshore winds and low atmo- spheric pressures accompanying a cyclone. In addition to generating large surface waves, the winds of the cyclone can push water toward the coast, holding it there as a set-up of the mean water level. The exceptionally low pressures of the storm system also contribute to increase the water level. (Water is going to rise 0.1 meter for every 10 millibars the central pressure is below the surrounding air pressure.) The storm surge may raise the water levels by several meters above the highest tides normal for the coastal zone, even covering areas generally not affected by wave attack. Considerable destruction results from the large waves superimposed on the exceptionally high levels since shoreline structures are now in the surf zone. Coastal erosion propagates. Additional to the aspect described above the continuous increase in the water level due to the greenhouse effect contributes to the coastal erosion in a slowly but significant way. Nevertheless the coastline of New South Wales is attacked by severe storms originating over the Tasman Sea. These storms are capable of causing rapid erosion along the south- eastern coastline. The low pressure systems from Tasman sometimes generate secondary lows, which intensify the storm systems. Under these conditions gale force winds, with a minimum wind speed of 50 kilometres an hour, are generated. In may 1974 for example a secondary low developed off the New South Wales coast, creating winds of over 140 kilometres an hour between North Sydney and Newcastle. This storm caused severe erosion, especially of Newcastle’s beaches (1). 5 Human Response to Natural Coastal Hazards

The most pressing problems associated with these natural hazards are the destruction of nature, property and the risk to life. These are usually the results of the accelerated erosion of the coast- line that occurs during intense storm periods. Attempts that have been made to find solutions to these problems are the following:

5.1 The Establishment of Buffer Zones

A study of the processes responsible for the shaping beaches and the impacts of storms along the coastline demonstrates the need to accommodate the fluctuations in beach width when de- veloping sites in the beach zone. This can be done by creating buffer zones. The width of the land needed to accommodate natural beach movements is the buffer zone. The establishment of buffer zones acknowledges that beaches fluctuate in extent as a result of the ’cut and fill’ processes that accompany certain weather conditions. Buffer zones mean that erosion can oc- cur without damaging property. These zones are effective methods of reducing storm damage, for not only are developments outside the areas subject to erosion, but also the natural reservoir of sand, the dunes are not isolated from the beach zone, and during calmer conditions the beach can be replenished naturally (2). In Figure 5.1, a description of a ’Buffer Zone’ is shown.

5.2 Beach Protection Systems

5.2.1 Seawalls

These are walls constructed from boulders and, or other structural devices along the beach, nor- mally fairly close to the surf zone. These walls are necessary in areas where development has taken place close to the beach zone and so property is threatened whenever the beach is attacked by storm waves. The disadvantage to be mentioned concerning seawalls is, that the sand be- hind the seawalls, in many cases a dune system is removed from the active beach system, thus limiting the amount of sand available for renourishing the beach. The limited sand supply may be quickly lost to the beach system and the level of beach reduced, so after storms, the beach cannot rebuilt and it may remain below water level. It may also alter nearshore topography and so the wave conditions (2).

9 5 Human Response to Natural Coastal Hazards 10

5.2.2 Groynes

Groynes are rock walls or other structures built out into the ocean. They are designed to alter the natural longshore movement of sand by acting as dams for sand. As sand is moved sideways by the longshore transport system, the groyne intercepts it. The sand is trapped on the updrift side, and the size of the beach is increased on this side of the groyne. The downdrift side of the groyne is starved of sand and the beach width there is reduced. Groynes help to stabilize the movement of sand along the coast. They also help to protect that part of the seabed closest to the shore from erosion. A problem caused by the use of groynes may be that they are designed to impound sand, which leads to an accumulation of sand on the updrift side and a reduced sand flow on downdrift side. If groynes extend beyond the breaker zone, they may divert sand into the offshore zone, where it may become lost to the beachface. They actually can cause deepening and steepening of the offshore seabed and increase the angle of wave approach, allowing sand to be moved along the beach for longer distances, and so increasing sand loss near the groyne. Longshore currents may be deflected seawards, creating rips, which drag large volumes of sand beyond the offshore zone and remain out of the local beach system, being transported to other coastal areas (2).

5.3 Sand Nourishment

This is the artificial return of sand to eroded beaches by pumping, Groynes will trap the sand being moved along the beach, but if the sand has been moved into the offshore zone and is not being returned to the shoreline, then sand is brought from other areas to replenish the beach. It is believed that this will not only return sand to a particular beach, but will also supply sand to the longshore transport system. Sand nourishment requires huge volumes of sand, and it is an expensive method of beach reconstruction. These enormous quantities of sand are obtained from other coastal areas, but the most satisfactory source of sand, because it adds sand to the system, is ’off-shore dredging’. This takes sand from the offshore zone, which is not a part of the present beach system. Sand pumped on to a beach from offshore is usually left at an unnaturally steep angle. Nature strives to reduce this by smoothing out the sand, that is, the sand is taken offshore. As much as 30-50 per cent of renourishment is lost in this way. It does not provide any long-term solutions to beach erosion, for the wave climate is still the same and leads to the need for ongoing renourishment at required intervals, every 5 to 10 years (2).

5.4 Dune Stabilization

Dunes that are well covered by vegetation are resistant to wind erosion, because the vegetation binds the sand. If vegetation is removed naturally by storms, wave overwash, strong winds, drought and bushfires, or artificially by clearing for building construction, the sand becomes mobile and can blow inland. Once it is away from the active beach zone, it is no longer capable of replenishing the shoreline. This is very important if beaches along the coastline are to be maintained, for the sand in these dunes provides much of the sand to the beach system. When 5 Human Response to Natural Coastal Hazards 11 sand is removed into the offshore zone, sand from the dunes can be used to replenish the beach face. Construction in this zone is also significant, for it effectively removes the sand from the system. If the dunes are reduced in size, storm waves can travel further inland and erosion is increased. Plants are also important, because they act as a trap for wind blown sand, which allows the dune to increase in size, providing a bigger reservoir for the beach system (2). 5 Human Response to Natural Coastal Hazards 12

Figure 5.1: Description of a Buffer Zone (2) 6 Three Southern Beaches of Sydney

This chapter deals with three southern beaches of Sydney who are located in the eastern suburbs of Sydney extending from Clovelly in the north, via Coogee, to Maroubra in the South. It describes the beaches and their surroundings and reveals facts about the coastal management of the Randwick City Council. The exact location of each of the three beaches, Clovelly, Coogee and Maroubra is indicated in figure 6.1.

Figure 6.1: Location of the southern beaches (1)

13 6 Three Southern Beaches of Sydney 14

6.1 Clovelly Beach

Clovelly Beach is one of the smallest and most unusual beaches in Sydney. The beach itself is only 70m long, backed by 100m of bare sand and edged by two walking path. However the entire beach is locked between two rocky ridges that extend like two arms for 300m seaward of the shoreline, and almost meet at their seaward end. The end result is an almost landlocked beach. Most wave energy is expended breaking on the beach on the northern side. What little wave energy gets into the bay eventually laps up against what is the lowest energy beach in Sydney. Clovelly Beach has essentially no waves and consequently no rips, which makes it to be a very save beach, as long as you don’t venture near the entrance of the bay, where the open ocean begins (5). Clovelly Bay has undergone a number of manmade modifications over the time, the most sig- nificant being the construction of concrete promenades over the natural rock to both, the north and the south sides of the bay. The cliffs, which line a large portion of the northern side of the bay, are composed of Hawkesbury Sandstone, which was mentioned in the introduction. The yellow sandstone darkened from the effects of weathering to the brown colour it has got today. The cliffs are generally vertical with some variations due to undercutting or collapse of walls. The cliffs extend from the headland to the northernmost point of the bay, creating a rugged coastline. The top of the cliffs are relatively flat, barren and exposed to strong winds. This environment is quite harsh, yet attractive due to its natural qualities and the spectacular views. The cliff tops are bounded to the west by a small stand of remnant vegetation. Uncontrolled access over the cliff top areas has led to the destruction of large areas of endemic vegetation. Consequently wind and water erosion has removed the fragile surface soils and exposed areas of clay subsoil. The sandy beach occurs at the western end of the bay, its width is restricted by surrounding slopes. Randwick City Council carried out a beach replenishment programme approximately nine years ago. Sand excavated from a building site in Bondi was transported and dumped on the Clovelly Beach, raising the sand level of the beach by nearly 0.5 meters. Because of the bay being protected against extremely large waves, a great deal of this sand still exists on the beach (5). The following three statements are quotations being made in the " Preliminary Investigation Report about the Clovelly Bay" (4), which reveal an appropriate description of the Coastal Exposure, the Breakwater Effect and the Sea wall reflection: • Coastal Exposure: The shoreline adjoining Clovelly Bay is exposed directly to wave action from the Tasman Sea and lacks protection from any natural or artificial off-shore structures. In turn, this wave action has progressively eroded the original rock formations giving rise to the essential form of the existing inlet with its narrow sheltered beach. • Breakwater Effect: It is understood, that the breakwater was installed across the mouth of Clovelly Bay approximately 67 years ago. This breakwater trapped a pool of water whose behaviour was largely independent of off-shore wave action. The partial destruc- tion of the breakwater has resulted in the transmission of wave energy and unimpeded tidal movement of water into the Bay. Accordingly, the conditions under which the inter- nal concrete structures in Clovelly Bay were developed no longer pertain. 6 Three Southern Beaches of Sydney 15

• Sea wall Reflection: The existing concrete sea walls within Clovelly Bay are nearly verti- cal and gradually neck towards the west. Water waves entering the Bay are able to reflect from the sea walls with little energy dissipation. The reflected waves interact, resulting in local peaks in excess of the incoming wave train. The necking of the body of water between the sea walls in the direction of the waves may increase the wave energy per unit width of the Bay can actually increase with distance from the breakwater. Investigating the area, two facts which are in urgent need to be improved have to be mentioned: The surface of the walkways are of mixed quality, with some areas being in a quite dangerous state due to missing concrete pieces, which contain exposed reinforcement within them and create trip hazards. The seawall along the southern side is in a poor condition and some parts require attention, as they are cracked and have collapsed undermining the slabs.

6.2 Coogee Beach

The name Coogee seems to have been derived from an Aboriginal word, which means "bad smell". This would be of course due to the decaying seaweed, which is washed up onto the beach, even in these modern times. It is one of Sydney’s smaller, more intimate beaches, yet in the summer it can be as crowded as any. Maybe not as famous as Bondi Beach, but a large number of eastern suburbs inhabitants prefer it to the more popular, high-profile Bondi. Coogee Beach is located about 12 kilometres south east of the Central Business District, is 400m long, and backed by a recently redeveloped park and promenade. In figure 6.2 certain area’s of the Coogee Bay are marked, which will be described on the following page (6). The sandstone seawall in the ’Goldstein Reserve’ behind the beach dates from the late 19th century, and is perhaps Coogee’s most visible evidence of the historical development of the site during the 19th century. Despite the removal of some of its length, in the late 1980’s, it survives virtually intact, and in remarkably good condition considering its age and exposure. The four sea pools in the describing area - Giles Bath and Ross Jones Pool at the ends of Coogee Beach, as well as the Women’s bath and Wylie’s Bath below the Grant Reserve- are listed by the National Trust. The ’Giles Bath’ has traditionally been regarded as part of the Giles Health Centre, built in 1928, and has significance because it is the largest of three pools in the Sydney region, which is predominantly made from natural rock. The ’Ross Jones pool’ was built in 1947 and has a unique design, which includes concrete piers, which extend beyond the top of the walls resembling to a castle. Due to a rather large amount of seaweed remaining in the pool it is not the aesthetic pool, as it once must have been, anymore. The pool of the ’Women’s Bath’ was constructed in 1886, substantially cut out of the rock shelf and retained with concrete walls in the south east corner. The pool has high aesthetic value due to its siting next to the cliff face and on the rock platform. It is the last remaining example of a segregated public swimming pool occurring on the New South Wales coast. Finally the ’Wylies Baths’ is one of the earliest swimming pools constructed on the Sydney coast, starting in 1902 and completing in 1907. It has got an elevated timber deck, built about eight meters above the pool. Although the original change facilities have been altered several times, the spectacular cliff side site, unique deck structure and association with the development of recreational facilities of the area have ensured that the complex has remained a well known landmark. 6 Three Southern Beaches of Sydney 16

Figure 6.2: Coogee beach subdivided in different areas

Nevertheless apart from these pools most of the people visiting the Coogee Bay certainly want to enjoy the beach. Waves coming towards the beach are quite low, making the beach a rather safe place. The reason Coogee is a safer beach, is due in large part, to the presence of Wedding Cake Island, located 800m off the beach. The island intercepts much of the wave energy out of the south east, resulting in an average breaker height of only 0.6m. This fact combined with the medium sized beach sand, produces a steep beach often fronted by a continuous narrow bar, usually devoid of rips, apart from those adjacent to each headland. Direct east swell however misses the island and produces higher seas (6).

6.3 Maroubra Beach

Maroubra Beach is located at the southern end of the eastern suburbs of Sydney, 12km south- east to the Central Business District. The name also originates from an aboriginal word, mean- ing ’Bay of Big Waves’. The beach is 1 km in length and can be subdivided into two parts. The northern half, curving to a rocky north headland is backed by a vertical seawall and prom- 6 Three Southern Beaches of Sydney 17 enade. In comparison, the southern half has a more natural form with a vegetated frontal dune backed by a grassed reserve. Apart from the very southern end the Maroubra Beach receives the full force of the Tasman Sea, producing the most hazardous beach in the area. The seawall at Maroubra was constructed during the 1920’s. Walls of this type are a quite familiar sight on many of the beaches in the region of Sydney. It is a concrete structure with a stepped upper sec- tion facing seaward. Facilities such as roads, pavilions, surf clubs and shops are built behind the seawall. The area behind the southern end of the beach was previously used as a garbage tip and hence the beach didn’t attract much usage. The tip was converted to a large open reserve and the frontal dune was preserved with its vegetation in poor condition. The beach has three zones of concentrated use, with its associated car park. These are located at the two ends and in a central section where swimmers are served by the facilities of the beach pavilion. The northern and cental section of the beach are dominated by 4 to 5 rip systems, which are particularly strong in the north and against the northern headland. Areas between are used by the board riders and are very popular as Maroubra has a reputation of having the most consistent surf south of the harbour (7). A beach management study found that the promenade was popular with beach users as a walking and viewing area. It also provided protection to the surf club and the car parking area. The Pavilion and car parking area had deteriorated to a state where they didn’t adequately cater for the users needs and detracted from the scenic quality of the beach. Works were proposed to improve the facilities with paving of the promenade, building a new pavilion, (which can be seen on the picture of Maroubra beach) and extensively landscaping the car park and surrounding areas. At the southern end, the opportunity existed to use more natural beach management techniques and provide facilities to enable the beach to be used to it’s full potential without adverse envi- ronmental impacts. Accordingly, the frontal dune was revegetated and fenced to control access across the dune. Crossing this fence line is supposed to be a crime and is punished by a high penalty of 40.000 AUD (7). The configuration of Maroubra Bay, with the major headland to the South and a lesser but still substantial headland to the North, allows a reasonable assumption to be made that the Maroubra Beach system is a closed one. This implies, that there are no net long-term losses or gains to the sand supply of the system, and that the quality of sand available for onshore and offshore movements is fixed. On the beach itself, the three beach zones described earlier are varied in their form and thus in their response to wave and wind forces. The southern and central zones, where the beach berm consists of sand down to indeterminate depths, recede and develop a steep beach face after significant wave attack. Later accretion in calm periods is quick to occur, from substantial available sand quantities observable offshore. The southern zone being more sheltered from storm waves usually recedes less than the central zone. Typical rips and channels are present all along the beach, but are particularly evident at the northern end of the central zone, where a rock shelf projects seaward of the normal waterline. It is on this rock shelf that the northern beach zone is perched. The beach berm here is a thin layer of sand overlying rock at very shallow depths. Even moderate swell conditions can remove a sufficient quantity of sand to render this zone unusable as a swimming resource, 6 Three Southern Beaches of Sydney 18 and subsequent accretion is slow to occur. The seawall along the northern part of the beach provides protection from storm wave attack of the beachside amenities, such as the pavilion, the promenade or the surf clubs, as well as a sand dune does along the southern half. In the northern half, the seawall merges into a structure known as the ’Colosseum’ in the northern beach zone. The Colosseum is protected by the rock shelf projecting seawards in front of it, and also provides its own protection by being founded on the shelf. However, in extreme storm events, broken water has flowed across the floor level of the structure. Nevertheless the beach is one of the most popular surfing beaches in Sydney and during the summer months is subject to intensive use. Because of its intrinsic scenic and recreational values, the beach is highly valued by the community. Despite these considerable attributes and the communities concern for its protection, Maroubra Beach has not achieved its potential as a premier coastal attraction and recreational resource. Its inherent natural qualities have been lost severely compromised by progressive urban development. Past attempts at redefining these qualities to achieve a resource complementary to the natural environment and capable of withstanding urban pressures have been largely unsuccessful. These pressures and the desire for enhancement of the site have created the need for a revised plan of management. Parts of this plan are shown on the appendix of the Maroubra Beach plan of management (7). 6 Three Southern Beaches of Sydney 19

Figure 6.3: Maroubra Beach, part of the ’Plan of Management’ (7) 7 The Coastline Hazards of these beaches

At the end of this report, the hazards are mentioned, which exists on the three beaches Clovelly, Coogee and Maroubra. In the appendix of this report there are 3 maps, which divide the areas of the beaches into certain zones. These zones characterize the hazards that exist in this certain sector, ranging from minor over moderate to serious kind of hazards. Most of these zones are shown in a picture, also to be found in the appendix. The description is been made from my point of view as well as I have tried to find a possible solution or precaution to decrease the hazard. Additionally to the figures in which the subdivision into the described zones of the beaches is given, 2 figures marking a general overview of every beach investigated are shown. The methods to work against these hazards are taken from "Coastal Management of NSW":

7.1 Clovelly Bay

7.1.1 Zone 1: hazard level: minor to moderate

Within the whole zone 1 (see figure 7.1) there are no buildings that may be endangered, so the hazard concerning the loss or collapse of buildings in this zone is minor or almost not existing . It is moderate to serious regarding the danger for people who may underestimate the strong winds that can occur during a storm surge. When they walk along the sandstone cliff during a strong storm they can either be blown over the edge of the cliffs, or be surprised by sudden cliff instability. Sings who prevent people from walking to near to the edge could be a possible precaution. Fences would be far to exaggerate because they disturb the beautiful view to the ocean. Otherwise as long as pedestrians stay on the footpaths along that zone the hazard is low! One hazard to be mentioned on the southern end of that zone is the storm water outlet, which could be a danger for incautious people who walk near to it during a storm and will be surprised by the large amount of water that suddenly will come out of the outlet. One possible solution could be to build the concrete pipe a little bit longer, to end up into the ocean.

7.1.2 Zone 2: hazard level: minor to serious

First of all the hazard for buildings in this area is minor because they are provided with enough space to the shoreline. More important in this zone is the danger for people who may walk along the concrete platform during a storm surge. They are endangered because of two reasons, first of all the really bad shape of the concrete which, apart from a storm surge, can cause serious injuries for people who would walk along the platform barefoot. The only improvement to be done on that hazard would be a complete new surface either with concrete or another material that is able to cope with the permanent oncoming water, like asphalt for example. Secondly,

20 7 The Coastline Hazards of these beaches 21

Figure 7.1: Zones of the Clovelly Bay the danger for people walking along the platform is to be mentioned. The existing breakwater stonewall on the northern side of the entrance of the bay cannot cope with the strong waves during a storm surge and will allow the large waves to flood the whole platform. Generally a good precaution would be a small (approx. 1m high) fence to protect the people to be drowned in to the ocean. The fence should be interrupted at the 4 stairs that allow people to step into the water.

7.1.3 Zone 3: hazard level: minor

This zone shows no danger, neither for people nor for buildings because the strong waves will have lost most of their power in the narrow bay. The only hazard to be mentioned is beach 7 The Coastline Hazards of these beaches 22

Figure 7.2: Clovelly Bay erosion, which takes place during a strong storm surge. Sand renourishment is the only method to prevent the beach from eroding to far.

7.1.4 Zone 4: hazard level: minor to serious

Zone 4 is very similar to zone 2 apart from the Clovelly Surf Life Saving Club (S.L.S.C.), which is located on the eastern end of the zone. It is build very near to the shoreline, on top of an almost vertical sandstone cliff, which is endangered to collapse due to cliff instability during a storm surge. A semi flexible seawall could be a possible precaution as well as special kind of concrete, that will last on an existing wall, over the surface of the cliffs to strengthen them and to make them last longer.

7.1.5 Zone 5: hazard level: low

The hazard within this zone is very low because there are no footpaths along the cliffs and as well there are no buildings in this sector that could be affected by a storm surge. The car park could even be regarded as a buffer zone in which the only loss could possibly be a forgotten car. To draw a conclusion on the hazards existing in the Clovelly Bay a proposal would be to in- crease, or to improve the existing breakwater seawall to decrease the power of the waves. Fur- 7 The Coastline Hazards of these beaches 23

Figure 7.3: Clovelly Beach thermore, the building of a similar kind of seawall on the southern end of the entrance of the bay would become necessary. They both would decrease all the hazards mentioned above.

7.2 Coogee Bay

7.2.1 Zone 1: hazard level: minor

The hazard in this zone (see figure 7.4) is low, because neither people nor buildings could be endangered by a possible cliff instability that may occur in this area during a storm surge. Footpaths as well as buildings are located in an appropriate distance to the edge of the cliff. 7 The Coastline Hazards of these beaches 24

Apart from that, signs warn the people to stay away from the unstable rock face are set along the edge, as well as a white wooden fence leads along the edge, to prevent people from falling.

Figure 7.4: Zones of the Coogee Bay

7.2.2 Zone 2: hazard level: serious

Much higher is the danger for people regarding zone two. Here, the footpath protected by a wooden fence leads exactly along the edge of the vertical sandstone cliff. People, who may walk along the path, or stand at the wooden fence to watch the storm takes place, could be surprised by a sudden collapse of the cliffs. The at the moment existing fence should be removed at least 2 meters further away from the edge of the cliff. Additionally signs have to mark, that it is prohibited to walk or sit on the space between the fence and the edge. Methods like for example concrete walls to stabilize the sandstone are an inappropriate solution, because it wouldn’t fit 7 The Coastline Hazards of these beaches 25

Figure 7.5: Coogee Beach, view from the south into the landscape, especially this part, which is visible to the whole beach. The further inland part of this zone, like the Barbecue Area or the parkland are not endangered at all.

7.2.3 Zone 3: hazard level: minor

This part of the Coogee Bay has a very low hazard concerning people and buildings. Besides the beach erosion, which can be regarded as a hazard, no really danger has to be mentioned. The vertical seawall, which has been rebuilt some years ago, protects buildings, as well as pedestrians who walk along the promenade. The beach itself can be seen as a buffer zone, in which the strong waves are supposed to lose at least some of their power, to be then reflected by the seawall. On the southern end of the beach, where the beach is rather narrow, there are concrete steps to break the waves, and an even higher seawall to guarantee the safety.

7.2.4 Zone 4: hazard level: moderate to serious

On the western end of this sector the Coogee Surf Life Saving Club is located exactly above the shoreline, build on a sandstone cliff, only about 1.5-2 meter above the mean high tide level. Therefore this building is in a very hazardous area off cliff instability and may collapse into the ocean in not too many years. The only precaution to protect the S.L.S.C. could be a flexible, or semi-flexible seawall consisting of rocks or concrete blocks to be placed in the ocean with the intention to break the strong waves and decrease their power. Otherwise, cliff stabilization with 7 The Coastline Hazards of these beaches 26

Figure 7.6: Coogee Bay, view from the north the help of concrete could be a possible precaution, but again the aspect of a rather uncomfort- able visual effect has to be regarded. The other building, or facility endangered in this zone, is the Wylie’s Baths, with a saltwater swimming pool on the same level as the ocean. Apart from swimming in the pool during a storm surge being very dangerous, also the building of the bath is highly endangered. It consists of a little kiosk, change rooms and a platform to take a sunbath. It is build on several rather thin wood columns, which are fixed with concrete in the sandstone cliff. When these cliffs will erode and be washed out by the ocean water during the time, they may be not fixed properly anymore and the building will collapse. Protection in the way of little concrete walls to prevent the water to reach the bottom of the columns could be a possible precaution. Otherwise the rest of this zone is not endangered.

7.3 Maroubra Bay

7.3.1 Zone 1: hazard level: moderate

The space between the edge of the sandstone cliffs and the nearest building or the footpath for the pedestrians is wide enough, measuring in between approx. 50-100m. Even if the nearly vertical cliff would suddenly collapse the danger for people or buildings is low. No precau- tions/preparations have to be worked out (see figure 7.7). 7 The Coastline Hazards of these beaches 27

Figure 7.7: Zones of the Maroubra Beach

7.3.2 Zone 2: hazard level: serious

The danger of destroying the buildings by a collapsing sandstone cliff is high, because the nearest house is only about 10m away from the edge of the vertical cliff, hence quite near to the shoreline.[picture 11] During a storm surge these sandstone cliffs can break and therefore erode into the ocean. Houses and other buildings will collapse and be destroyed. Also the danger for people like pedestrians or drivers on the street is very high because they can be surprised by a sudden collapse of the cliffs. People do not expect cliff instability while watching the storm from the footpath and underestimate the danger.[picture 12] The measurement against this hazard could be a flexible or semi-flexible seawall to prevent the really strong waves to reach the sandstone cliff with all their power and hence to decrease the possible cliff instability. Nevertheless, road signs should prevent people from walking along the footpath during a storm surge. 7 The Coastline Hazards of these beaches 28

Figure 7.8: Maroubra Beach

7.3.3 Zone 3: hazard level: moderate to serious

The North Maroubra Surf Life Saving Club as well as the Beach Pavilion are highly endangered during a strong storm surge because they are both almost unprotected in any way. The only precaution that slightly prevent the waves to reach these buildings are two concrete stairs, the first one with 4 and the second one with 3 steps. It is rather easy for the strong waves to reach these buildings because the shallow and not very wide reach cannot be seen as a buffer zone. A possible precaution could be a vertical seawall on the platform between the two stairs. It might be rather difficult to add a concrete wall to the existing concrete platform in short distances. The waves would break on the first stair and would be reflected by the new seawall to protect the two buildings. The danger for people or pedestrians is rather low, because the danger won’t come abrupt and is obviously predictable visually. They can see the large waves approach to the platform more and more. Last but not least beach erosion takes place so that even the now more or less existing buffer zone of the beach will decrease in the future.

7.3.4 Zone 4: hazard level: minor to moderate

There is almost no danger either for buildings in this zone or for people. The only existing building is the South Maroubra Life Saving Club S.L.S.C, which is located with enough space to the shoreline. Also people are not endangered by a possible storm surge because there are no ways or footpaths leading through the dunes that lead from the beach to the hinterland. The only hazard may be beach erosion and the loss of the dunes caused by the lack of vegetation 7 The Coastline Hazards of these beaches 29

Figure 7.9: Maroubra coast on the dunes. Methods against this procedure can be dune stabilisation by providing the dunes with enough vegetation and sand renourishment to restrain the appropriate amount of sand on the beach.

7.3.5 Zone 5: hazard level: minor to moderate

The hazard in this particular zone is quite low, because here are neither buildings nor footpaths along the edge of the cliffs. The footpaths that lead through this zone are built within an ap- propriate distance from the edge. Only incautious people who walk to or along the edge of the sandstone cliffs could be endangered by strong winds or a possible cliff instability resulting from a storm surge. No precautions have to be done except for signs to make the people realize the danger while walking on the edge of the cliffs.

7.4 Final Statement

Finally I want to say, that the investigation I did in this report has been very interesting for me, I definitely learned a lot about coastal erosion and beach processes. Also the research about the beaches in the Randwick City Council and outside on the beaches themselves has been very interesting, because I have become a more deeper insight into the beaches and their surroundings, than a ’usual’ beach visitor. The problems of coastal erosion and cliff instability 7 The Coastline Hazards of these beaches 30 has become a very dangerous hazard, especially along the coast of New South Wales. Methods have to be done in the near future to prevent this piece of beautiful nature from being destroyed. The public awareness, which is rather low concerning these problems, has to be increased in order to let the people who live along the coast realize how dangerous it could be to build their houses straight along the edge of the cliff. Bibliography

[1] Beaches of the NSW Coast; Andrew D. Short;1985

[2] History and Heritage of Coastal engineering; Nicholas C.Kraus; 1989

[3] CRC Handbook of Coastal Processes and Erosion; Paul D. Komar; 1996

[4] Randwick City Council Preliminary Investigation Report; 1996

[5] Clovelly Beach, Plan of Management; 1997

[6] Coogee Beach, Plan of Management; 1995

[7] Maroubra Beach, Plan of Management; 1995

[8] Randwick City Council Library: Maps; 1984

[9] Waves, tides and Shallow-Water Processes; Open University Course Team; 1997

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